The proposed research will concern the course of development of auditory processing in brainstem centers and the susceptibility of this development to changes induced by manipulations of the early sound environment. Rats will serve as experimental subjects, the onset and sequence of unit acitivity at the VIIIth nerve, cochlear nucleus, and inferior colliculus being observed through acute unit recording. Manipulations of the auditory history of individual animals will include deprivation and augmentation of the normally experienced sounds. The objective is to characterize the neural events leading to adult auditory processing and determine their vulnerability to plausible extremes of sound experience.